IMPROPER INFLIGHT PLANNING/DECISION BY THE STUDENT PILOT (PILOT-IN-COMMAND), AND HIS FAILURE TO MAINTAIN ADEQUATE AIRSPEED, WHICH RESULTED IN A STALL. FACTORS RELATED TO THE ACCIDENT WERE: PHYSICAL IMPAIRMENT OF THE STUDENT PILOT/OWNER/OPERATOR FROM CARBON MONOXIDE, MOUNTAINOUS TERRAIN, AND HIGH DENSITY ALTITUDE.